This invention relates to an improved coupling for articulated vehicles that reduces or prevents jack-knifing of such vehicles when braking hard or on slippery surfaces. The articulated vehicles to which this invention relates and the words "articulated vehicle" will henceforth be used to mean any combination of a tractor vehicle connected, by means of a coupling device that is commonly referred to as a fifth wheel, to a load carrying trailer. The tractor conventionally comprises a chassis supported by at least two pairs of coaxially mounted wheels of which at least one pair are driven by a prime mover by means of conventional automotive transmissions and the other coaxial pair are steerable by a driver from the cab area located on the chassis. The trailer conventionally comprises a load carrying enclosure supported by at least one pair of coaxially mounted wheels that is connected to and partly supported upon the tractor by means of the fifth wheel coupling which is attached to the tractor and releasably secures the load carrying trailer to the tractor vehicle by engaging a vertical king pin attached to the trailer about which the load carrying trailer may turn relative to the tractor.
Articulated vehicles are particularly useful because a single tractor may be used to transport a number of different trailers thereby saving turnaround time when the tractor vehicle would otherwise be unuseable during loading and unloading of the trailer. While articulated vehicles have well recognized merits, they have a common drawback in that the trailer is inclined to "jack-knife" where the wheels of the articulated vehicle lose traction during hard braking or on slippery surfaces or both. By "jack-knife" is meant the uncontrolled rotation of either the tractor or the trailer about the king pin of the fifth wheel coupling unit. As a result of jack-knifing, the articulated vehicle continues to move in the direction of travel with either the tractor or trailer unit swung about the king pin of the fifth wheel coupling so as to be located at an angle to the direction of travel or, alternatively, the trailer unit of the articulated vehicle swings slowly about the king pin.
Jack-knifing usually occurs where all four wheels of the tractor portion of the articulated vehicle lose traction and the tractor skids in a straight line until any slight imbalance in the rolling resistance of the wheels imparts a force to the tractor or trailer having the component normal to the direction of travel causing the tractor portion of the vehicle to swing slowly but uncontrollably about the king pin of the fifth wheel coupling between the two units into the fully jack-knifed position. Jack-knifing may also occur where the rear wheels only of the tractor portion of the vehicle lose traction. In this condition, any force normal to the direction of travel will cause sudden and serious jack-knifing of the articulated vehicle that is very difficult if not impossible to correct. This type of instability is the cause of many fatal accidents due to the abrupt manner in which the articulated vehicle can sweep across the path of oncoming traffic while moving at operating speeds. Another extremely dangerous jack-knifing condition occurs where the trailer wheels lose traction and the trailer swings from side to side about the fifth wheel coupling thereby obstructing other lanes of traffic. In either of the latter types of instability, operation of the vehicle brakes tends to aggrevate rather than alleviate the tendency to jack-knife.
Various proposals have been made for inhibiting or controlling the jack-knifing action of articulated vehicles and some of these systems have proved acceptable in use, however, most of the proposals are complex, expensive and have other shortcomings. Some of the proposals take up space inside the trailer, others require very high hydraulic pressures to operate the brake means with attendant problems of high pressure hosing, seals, maintenance and adjustment. Still others fail to operate well during foul weather. An object of the present invention is to provide an anti jack-knifing device that is simple in concept, easy and inexpensive to fabricate, adaptable to any tractor-trailer configuration, efficient in use and operable under all weather conditions.
According to the invention an anti jack-knifing device for coupling a powered tractor vehicle to a load carrying trailer includes a turntable supported for rotation about a substantially vertical spindle located and adapted to be fixed to the rear of the said tractor vehicle so that the vertical axis lies on the longitudinal center line of the tractor vehicle, a releasable coupling means that releasably connects and locates the load carrying trailer with respect to the turntable whereby rotation of the trailer with respect to the tractor will cause corresponding rotation of the turntable and annular brake surface as a unit about said vertical spindle. The annular brake surface is braked by a brake means that may be connected by valve means to the braking system of the articulated vehicle so as to prevent or inhibit rotation of the turntable and trailer during deceleration of the articulated vehicle. The said brake means is secured to a base adapted to be attached to the rear frame of the tractor vehicle. The turntable is secured to the said annular braking surface for rotation about said vertical spindle and supported by strips of any suitable bearing material attached to the upper surfaces of the rear frame of the tractor vehicle. The annular brake surface and brake means may be provided by using a standard automotive wheel hub and automotive drum or disc brake assembly. The trailer is connected to the tractor by means of a standard fifth wheel coupling, the horizontal pivot of which is arranged upon the turntable so as to be normal to the direction of travel. Any suitable locating devices keep the turntable aligned with respect to the trailer so that any rotation of the trailer with respect to the tractor will cause a corresponding rotation of the turntable. In the preferred embodiment, two side rails are attached on either side of the fifth wheel coupling unit so as to lie parallel to the longitudinal center line of the wheel tractor vehicle. Complimentary channel shaped locating members are adapted to be attached to the underside of the front of the trailer and arranged so as to engage and mate with the two side rails connected to the turntable when the tractor is coupled to the trailer. Operation of the braking system of the articulated vehicle would normally engage the braking means to prevent articulation of the tractor and trailer units but, at slow speeds where articulation is essential to manoeuverability or in the event of serious skidding or jack-knifing prior to application of the coupling brake means, the coupling breaking means can be disengaged by operating the valve means .